Supplementary Materials
Table of Contents
SI │ Materials and Methods……….……… 2
SII │ Supplementary Notes and Figures ……… 6
SIII │Supplementary Tables……….… 43
SIV │Supplementary References……….… 46
1
SI │ Materials and Methods
Catalyst preparation
ZnO samples are from Sigma-Aldrich and used without any modification. ZnO mainly used in this work has a reference number of 96479. Commercial pristine ZSM-5 zeolites (NH4-form) with different Si/Al ratios were purchased from ZEOLYST (CBV 28014, CBV 8014, CBV 3024E, CBV 2314). The zeolites were calcined in a static oven for 6 h at 550 °C with a heat ramp of 2 °C min−1, to obtain their protonic forms. Catalysts were denoted as HZ-x, where x stands for the corresponding Si/Al ratio (140, 40, 15, 12).
Typically, HZSM-5 with a Si/Al ratio of 140 (HZ140) was used unless otherwise mentioned. The Zn-ion exchanged HZSM-5 zeolites were obtained through stirring NH4-form ZSM-5 powder in a dilute zinc nitrate solution (0.05 M, m(liquid)/m(solid) = 50) at 50 °C for 6 h, and then washing thoroughly and drying. The ion-exchanging operation was repeated three times, and finally the dried sample was calcined at 550 °C for 6 h. The corresponding catalysts were denoted as ZnHZ-x to indicate the presence of Zn sites and the Si/Al ratio (x = 15 or 12).
Typically, the powder samples were pelletized and crushed into 150-250 µm particles prior to any catalytic tests. The powder mixture of ZnO and zeolite was prepared by mixing and grinding the two components in an agate mortar for 10 min before pelletizing. The mass ratio of the two components (ZnO and zeolite) was fixed at 1:1 in this work unless otherwise mentioned. For the granule mixture, the granules of ZnO and zeolite were simply mixed together by shaking in a vessel. For the dual bed sample arrangement, the granules of different components were simply separated by placing an inert layer of quartz wool ~ 3 mm in thickness between them.
Catalyst characterization
The Si/Al ratio and Zn loading of zeolite catalysts were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis. Samples were digested in a solution containing HF and HNO3
and experiments were performed on a ICP-OES Agilent 5110 instrument. Transmission Electron Microscopy (TEM) micrographs were acquired using FEI® Tecnai Twin microscope in the bright field mode, with the filament voltage set to 120 kV. High-angle annular dark-field scanning transmission electron microscopy (HAADF–STEM) analysis and energy dispersive X-ray (EDX) elemental mapping of the samples were carried out with an FEI Titan G 2 80-300 kV electron microscope operated at 300 kV. All solid-state NMR experiments related to 1H and 13C were conducted on an AVANCE-III console equipped with a 3.2 mm HXY probe in the double channel 1H, 13C mode on a Bruker 600 MHz wide-bore magnet. All experiments were conducted at room temperature (298 K) and at a MAS frequency of 20 kHz. 1H and 13C chemical shifts were referenced externally to adamantane. The 1D 1H-13C cross-
2
polarization (CP) spectrum was recorded with a 4 s recycle delay and a 33 ms acquisition time. During the CP step, 1H CP spin-lock pulses centered at 75 kHz were linearly ramped from 70 to 100% and the 13C RF field was matched to obtain an optimal signal. The 1D direct excitation (DE) spectrum was acquired with a 5 s recycle delay and a 10 ms acquisition time. 2D 13C-13C spectra were acquired with a 2 s recycle delay, 10 ms (F2) acquisition time and an accumulation of 256 scans. 13C-13C mixing was achieved through proton driven spin-diffusion using phase-alternated-recoupling-irradiation-schemes (PARIS) for 120 ms. 70 kHz SPINAL64 1H decoupling was applied during both direct and indirect dimensions. 2D
1H-13C frequency switched Lee-Goldburg (FSLG) heteronuclear correlation spectroscopy (HETCOR) spectra were recorded with a 3 s recycle delay, 15 ms (F2) or 1.6 ms (F1) acquisition time and an accumulation of 64 scans. All NMR spectra were processed with Bruker Topspin 3.5 and analyzed using POKY software1.
In situ planar laser-induced fluorescence (PLIF) experiments
In situ planar laser-induced fluorescence was employed to measure CH2O. A continuous optical reactor system was implemented to collect the LIF signals via 2 cm diameter quartz window. The setup was represented in Fig. S8. A thin layer of catalyst was held by a quartz plate, which was then horizontally placed at the center of the reactor and observed from the quartz window. The catalyst was pretreated with N2 at 500 °C for 1 h and then cooled to reaction temperature of 450 °C. Methanol was vaporized at 25 °C and carried by a N2 flow to the reactor. The formaldehyde is excited by the third harmonic of a Nd:YAG laser (Brilliant b, Quantel) at the wavelength of 355 nm. A cylindrical lens (500 mm focal length) was used to reshape the laser beam into a vertical sheet (∼100 µm in thickness) over the surface layer of the catalyst. The 2D CH2O LIF signal was collected by a 105 mm Sodern UV lens with band-pass filter (Semrock, FF01-CH2O) and imaged by an intensified charge-coupled device (ICCD) camera (PI-MAX3 1024i, Princeton Instruments). In order to increase the signal to noise ratio, images were accumulated 10 times before each readout of the camera and 50 acquisitions were taken and averaged for each test condition. Images taken in a flow of nitrogen for each operating conditions, provided the background signal. In order to compare the trend of CH2O signal, simulations were also performed using CHEMKIN- PRO, focusing on the same reactive region above the catalyst surface.
Operando photoelectron photoion coincidence spectroscopy (PEPICO) experiments
Operando photoelectron photoion coincidence spectroscopy (PEPICO) experiments were carried out using the CRF-PEPICO endstation at the vacuum ultraviolet beamline of the Swiss Light Source of the Paul Scherrer Institute, Switzerland. CH3OH was vaporized at 25 °C under Ar atmosphere and dosed by a set of digital mass flow controllers into a heated tubular quartz reactor (2 mm internal diameter) mounted
3
on a molecular beam source in the source chamber. The PEPICO experiments were conducted at reactor inlet pressures of 5×10−1 bar. Catalyst was loaded into the reactor and quartz wool was used to secure the sample during testing. The catalyst was dried in Ar flow at 500 °C for 1 hour prior to operating PEPICO experiments and an empty quartz reactor was used for reference. At the reactor outlet, reaction products, intermediates, and unconverted reactants form a molecular beam. As the beam passes through a skimmer, monochromatic vacuum ultraviolet (VUV) radiation ionizes the molecules. The resulting photoelectrons and photoions are accelerated in opposite directions by a constant electric field, which is detected in delayed coincidence. Time-of-flight (TOF) mass spectrometry is used to determine the species of photoions by determining the ratio of mass to charge (m/z). The photoion mass-selected threshold photoelectron (ms-TPE) spectra are derived by integration of electrons with low kinetic energy ((5-10)
×10−3 eV). By comparing ms-TPE spectra with Franck-Condon simulations, vibrational fingerprints in the spectra identify the molecular structure and enable isomer-selective detection. More details about PEPICO experiments can refer to Supplementary Note 5 provided in the Supplementary Information file.
Methanol-to-aromatic (MTA) tests
Catalytic experiments for methanol-to-aromatic (MTA) tests were performed in a four channel Flowrence® XD from Avantium2. Prior to the reaction, the catalyst was mixed with SiC and pretreated with N2 at 550 °C for 2 h. Reaction temperatures from 400 to 500 °C were tested and methanol was diluted in N2 to a constant molar MeOH:N2 ratio of 1:3 at ambient pressure. The reaction products were analyzed on line by means of gas chromatography (GC) in an Agilent 7890B with three detectors: 2 FIDs and 1 TCD. Methanol conversion (X, %), selectivity (S, %) and yield (Y, %) of each i product are defined as follows:
X=CMeOH
¿−CMeOHout−2× CDMEout CMeOH
¿
×100 1
Si= i ×Ci
CMeOH¿−Coxyout×100 2
Yi=Si× X
100 3
where CMeOH
¿ , CMeOHout , CDMEout and Coxyout are the concentrations determined by GC analysis of methanol in the blank, and in the reactor effluent, respectively. A total selectivity to monoaromatics is calculated, including benzene, toluene, xylenes (BTX), ethylbenzene, C9 and C10
4
aromatics. Carbon balance (> 95%), as determined by comparing the molar quantity of all species containing carbon in the inputs and outputs, was used to evaluate the reliability of reactivity data.
Co-feeding experiments
Experiments with co-feeding unlabeled chemicals were performed in a four channel Flowrence® XD from Avantium. The feeding carbon atoms contain 2/3 of those from MeOH or DME (dehydration species from two MeOH molecules), and 1/3 from HCHO. The mixture of MeOH and H2O (MeOH/H2O
= 3/2.8), the mixture of MeOH/formalin (MeOH/HCHO/H2O = 2/1/2.8), and pure dimethoxymethane (quasi DME/HCHO = 1/1) were tested at ambient pressure. All reactions were performed based on the same carbon feeding rateC feeding rate, 0.015 g h−1.
Experiments with co-feeding H13CHO were performed in a reactor connected to a mass spectrometer.
The catalyst was pretreated with He at 500 °C for 1 h and then cooled to a reaction temperature of 450 °C.
The mixture of MeOH and H13CHO (molar ratio, MeOH/ H13CHO = 20, 10 or 5) was vaporized at 25 °C and carried by a He flow to the reactor. After stabilization, the gas phase products were analyzed by a Transpector CPM Mass Spectrometer. The m/z 54 and m/z 55 represent unlabeled and labeled 1,3- butadiene, respectively. Fragmentation and data analysis were referred to the database of the National Institute of Standards and Technology (NIST).
Catalyst tests for propylene conversion and propane dehydrogenation
Catalytic tests for propylene conversion and propane dehydrogenation were also performed in a four channel Flowrence® XD from Avantium. Prior to any reaction, the catalyst was pretreated with N2 at 550
°C for 2 h. Propylene was diluted in N2 to a constant molar C3H6:N2 ratio of 1:3 and catalytic tests were conducted at 450 °C under ambient pressure. For propane dehydrogenation, propane was diluted in N2 in advance (20% in N2) and the tests were conducted at 450 °C or 550 °C under ambient pressure.
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SII │Supplementary Notes and Figures
Supplementary Note 1│ For the route displayed in Fig. 1A, methanol molecules are first transformed into light olefins (C2=-C4=) on Brønsted acid sites in zeolite via a traditional methanol-to-olefin reaction.
Olefin methylation and/or oligomerization leads to chain growth, producing heavy olefins (> C4=). The subsequent cyclization of heavy olefins leads to (methylated) cyclic alkanes, which result in cyclic olefins either by hydrogen transfer reactions forming inactive paraffins, or via direct dehydrogenation reactions catalyzed by metal sites forming hydrogen. In a similar way, cyclic olefins can be transformed into monocyclic aromatics by hydrogen transfer or dehydrogenation reactions on acids or metals, respectively.
The presence of acids and metals contributes to the unwanted transformation of monoaromatics to polyaromatics. Formaldehyde is generally considered a crucial species accelerating catalyst deactivation.
It can be produced on Brønsted acid sites by methanol disproportionation3, or on aluminum-based Lewis acid sites by hydrogen transfer with alkenes4. Both of them lead to the formation of inactive paraffins. In addition, formaldehyde can be generated directly from methanol dehydrogenation on metal sites, producing hydrogen in parallel5. Catalyzed by acid sites, the alkylation reactions between formaldehyde and active monoaromatics result in highly active benzyl carbenium ions, which easily react with olefins or monoaromatics and are rapidly converted into polyaromatics with the aid of acid and metal sites (33).
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Fig. S1. Stability test of HZ140 for 120 h. Reaction conditions: HZ140 weight, 20 mg; 450 °C; MeOH rate, 0.04 g h−1; MeOH/N2 molar ratio, 1:3; 0.1 MPa.
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Fig. S2. Reaction temperature screening over different catalysts packing modes. (a) Catalyst with only zeolite (HZ140). (b) Catalyst with zeolite packed below ZnO, separated by an inert layer of quartz wool. (c) Catalyst by mixing granules of zeolite and ZnO of 150–250 μm size. (d) Catalyst containing zeolite and ZnO well mixed and powder grinded in a mortar. Reaction conditions: HZ140, 20 mg; ZnO, 20 mg; MeOH rate, 0.04 g h−1; MeOH/N2 molar ratio, 1:3; 0.1 MPa.
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Fig. S3. Effect of zeolite Si/Al ratio. Packing modes: powder mixture. All zeolite components were obtained by calcining commercial Zeolite Socony Mobil 5 (ZSM-5) zeolites at 550 °C. Reaction conditions: Zeolite, 20 mg; ZnO, 20 mg; 450 °C; MeOH rate, 0.04 g h−1; MeOH/N2 molar ratio, 1:3; 0.1 MPa.
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Fig. S4. Effect of ZnO particle size. (a) Powder X-ray diffraction pattern of ZnO (used in the main work, ~400 nm) and ZnO (<100 nm). (b) TEM image of ZnO (<100 nm). (c) Catalytic reaction result using ZnO (<100 nm) as one component of powder mixture. All zinc oxide samples are commercial from Sigma-Aldrich and used without any modification. The refence number for ZnO used in the main work is 96479, and that for ZnO (<100 nm) is 544906. Reaction conditions: HZ140, 20 mg; ZnO (<100 nm), 20 mg; 450 °C; MeOH rate, 0.04 g h−1; MeOH/N2 molar ratio, 1:3; 0.1 MPa.
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Fig. S5. Effect of ZnO/Zeolite mass ratio. The weight of zeolite is fixed while that of ZnO is varied.
The selectivity is the average result of the first 10 h test. Reaction conditions: HZ140, 20 mg; ZnO, 10-80 mg; 450 °C; MeOH rate, 0.04 g h−1; MeOH/N2 molar ratio, 1:3; 0.1 MPa.
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Fig. S6. Effect of contact time (calculated based on zeolite weight). The methanol flow is fixed while the total amount of catalyst (ZnO/Zeolite mass ratio = 1:1) is varied. The selectivity is the average result of the first 10 h test. Reaction conditions: total weight of catalyst, 10-160 mg; 450 °C; MeOH rate, 0.04 g h−1; MeOH/N2 molar ratio, 1:3; 0.1 MPa.
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Supplementary Note 2│The powder mixture of HZ140 and ZnO displayed the best performance at 450
°C (Fig. S2). On one hand, the selectivity of monocyclic aromatics was the highest (around 40%). On the other hand, during stable reaction period, COx was no longer produced and the selectivity to C2-C4
paraffins was only around 3%. The Si/Al ratio of zeolite can steer reactions in different manners (Fig.
S3). When the amount of acid sites increased, the traditional hydrogen transfer reactions were enhanced, and as a result, more light paraffin were produced. Also because of the olefin consumption in the above way, formaldehyde would undergo further dehydrogenation and thus more COx were produced. Reducing the size of ZnO nanoparticles provides more exposable metal active sites, but this promoted deep methanol dehydrogenations (Fig. S4). As a result, more valueless COx were produced. When the mass ratio of ZnO/HZ140 was 1:1, the highest selectivity was achieved (Fig. S5). With the increase of contact time, the selectivity gradually increased and then stabilized (Fig. S6). When contact time was at 0.5 h (WHSV = 2 h-1), we obtained a high selectivity with a high methanol throughput.
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Fig. S7. Stability test of ZnO+HZ140 for 120 h. Reaction conditions: HZ140, 20 mg; ZnO, 20 mg; 450
°C; MeOH rate, 0.04 g h−1; MeOH/N2 molar ratio, 1:3; 0.1 MPa.
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Fig. S8. Experimental configuration for 2D HCHO-PLIF imaging.
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Fig. S9. 2D HCHO-PLIF imaging near the ZnO surface over 100 minutes. The reactant gases go from left to right.
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Fig. S10. 2D HCHO-PLIF imaging near the HZ140 surface over 100 minutes. The reactant gases go from left to right.
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Fig. S11. 2D HCHO-PLIF imaging near the catalyst ZnO+HZ140 surface over 100 minutes. The reactant gases go from left to right.
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Fig. S12. HCHO-PLIF signal as a function of reaction time over different catalysts. The signal is extracted from a fixed location as indicated by a red rectangle. The reactant gases go from left to right.
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Supplementary Note 3│The 2D HCHO-LIF imaging results indicate that HCHO can be produced and consumed via different pathways. Using ZnO as catalyst, HCHO can be produced via CH3OH dehydrogenation, with the formation of H2. However, the further dehydrogenation of HCHO led to CO and H2. As a result, at the beginning of reaction, HCHO was not observed. With the deactivation of ZnO, the dehydrogenation of HCHO was suppressed and thus HCHO signal started to increase. Using HZ140 as catalyst, HCHO was produced via CH3OH disproportionation, with the formation of CH4. The observation of HCHO only at the very initial stage of reaction is consistent with previous MTH studies on the first C-C bond formation6. With the formation of hydrocarbon pool species and the establishment of dual cycles, CH3OH mainly participates in the whole reaction process via other pathways, such as dehydration and methylation reactions. As a result, the HCHO signal disappeared quickly. In contrast, for the mixture ZnO+HZ140, HCHO was observed during the whole measurement. HCHO was mainly produced via CH3OH dehydrogenation catalyzed by ZnO. However, compared to pure ZnO catalyst, HCHO signal over the mixture was much lower, indicating that HCHO was formed but quickly consumed. A possible explanation is that HCHO can react with olefins produced by zeolite to form dienes and then aromatics7. Although the flow direction resulted in the accumulation of formaldehyde at the right in all cases, over the mixture, no matter from space or time, formaldehyde distribution was more homogeneous and stable. Note that COx (or HCHO) was not always present in the effluent during the standard reaction tests to evaluate the catalytical performance of catalysts. The difference should be related to different structural configurations of reactors. For our standard catalytic tests, catalyst was loaded in a tubular reactor as a column and in situ generated HCHO must undergo subsequent reactions when flowing downstream.
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Fig. S13. Propylene reaction results over different catalysts. (a) Conversion of propylene. (b) H2
generation. (c) Product distribution. Reaction conditions: HZ140, 20 mg; ZnO, 20 mg; 450 °C; C3H6 rate, 0.05 g h−1; 0.1 MPa.
Supplementary Note 4│The Zn-containing HZSM-5 catalysts have been widely explored in the methanol-to-aromatics reactions due to the dehydrogenation ability of Zn species . Based on the traditional route, methanol aromatization process mainly includes two main steps: methanol-to-olefin and olefin-to-aromatic. It is widely accepted that the dehydrogenation function of Zn is mainly displayed in the second step, namely, the olefin-to-aromatic step8. Here, we use propylene transformation as a probe reaction to study the role of ZnO particles in olefin transformation. At 450 °C, ZnO particles show no activity in propylene transformation. Due to the high Si/Al ratio, the zeolite (HZ140) only shows a limited activity, with a conversion value being 35%. Adding ZnO increased the conversion to above 60% (Fig.
S13a). A possible explanation is that ZnO promotes the transformation of intermediate species and could drive the reaction direction from propylene to the final product. This is related to the dehydrogenation ability of ZnO, as confirmed by generation of more H2 (Fig. S13b). However, aromatic selectivity was only around 2% over mixture catalyst, which is much lower than the value using methanol as reactant.
This indicates that the promoting role of ZnO in the olefin transformation did not contribute much to the aromatics formation. Therefore, there should be another reason to explain why using the mixture catalyst can boost aromatic production during methanol conversion.
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Fig. S14. Transformation of the ratios between different reactants. (a) MeOH and formalin. (b) Dimethoxymethane (DMM).
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Fig. S15. Schematic diagram of PEPICO endstation used for methanol conversion.
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Fig. S16. Principle of PEPICO to detect and identify species. Mass spectrometry with tunable vacuum ultraviolet (VUV) synchrotron radiation is the first experimental approach to detect species, and photoion mass-selected threshold photoelectron (ms-TPE) spectroscopy reveals spectroscopic fingerprints to assign all isomers unequivocally.
Supplementary Note 5│ Operando photoelectron photoion coincidence spectroscopy (PEPICO) experiments were carried out using the CRF-PEPICO endstation at the vacuum ultraviolet beamline of the Swiss Light Source of the Paul Scherrer Institute, Switzerland. As shown in Fig. S15, a heated microreactor is coupled with a gas sampling setup to enable the detection of species during methanol conversion. At the reactor outlet, reaction products, intermediates, and unconverted reactants form a molecular beam. As the beam passes through a skimmer, monochromatic vacuum ultraviolet (VUV) radiation ionizes the molecules. The resulting photoelectrons and photoions are accelerated in opposite directions by a constant electric field and detected in delayed coincidence. Time-of-flight (TOF) mass spectrometry is used to determine the relative ratio of the species of interest (see formaldehyde Fig. S16).
The photoion mass-selected threshold photoelectron (ms-TPE) spectra (Fig. S16) are derived by
24
integration of electrons with low kinetic energy ((5-10) ×10−3 eV). All species are isomer-selectively identified by comparing the ms-TPE spectra with Franck-Condon simulations or reference spectra9,10. CH3OH was vaporized at 25 °C and 2 bar under Ar atmosphere and dosed by a set of digital mass flow controllers into a heated tubular quartz reactor (2 mm internal diameter) mounted on a molecular beam source in the source chamber. The PEPICO experiments were conducted at reactor inlet pressures of 5×10−1 bar. Catalyst was loaded into the reactor and quartz wool was used to secure the sample during testing. The catalyst was dried in Ar flow at 500 °C for 1 hour prior to operating PEPICO experiments and an empty quartz reactor was used for reference. Quartz reactors were heated by heating wires mounted on heating sleeves and powered by DC constant current supplies (Voltcraft). At the midpoint of the heater assembly, a type K thermocouple was attached to the outside reactor wall to monitor its temperature. The pressure in the source chamber surrounding the reactor outlet was 2×10−8 bar. The central part of the molecular beam leaving the reactor was skimmed (2 mm orifice) upon entering the analysis chamber, operating at a pressure of 2×10−9 bar. The synchrotron vacuum ultraviolet (VUV) radiation was collimated and dispersed by a 150 mm−1 grating and focused onto the exit slit (200 µm) located in the gas filter. In the 8.5-14 eV photon energy range, higher order radiation was suppressed by using an Ar/Ne/Kr mixture (30 vol.% Ar, 10 % Kr, in Ne 5.0) at 1×10−2 bar over an optical length of 10 cm. The photon beam crossed the skimmed molecular beam from the reactor in the ionization region.
Photoions and photoelectrons produced upon ionization were accelerated vertically in opposite directions by a constant electrical field of 230 V cm−1 and were velocity map imaged onto two delay-line anode detectors (Roentdek, DLD40), and detected in delayed coincidence11. Since the electrons have a much shorter flight time (ca. 100 ns) than the ions, they are used as start signal for the ion time-of-flight (TOF) detection in a multi-start multi-stop coincidence scheme. The photon energy was scanned in 0.03 eV steps and averaged 120 s in the photoion mass-selected threshold photoelectron (ms-TPE) spectrum scans. The kinetic energy resolution of the electrons was set to (5-10) ×10−3 eV and faster electrons with a negligible off-axis momentum component were subtracted using the approach by Sztáray and Baer12. The false coincidence background baseline was also subtracted from the threshold ionization mass spectra.
Gaussian16 was utilized to calculate ionization energies, equilibrium structures and vibrational modes.
Adiabatic ionization energies were computed by optimizing the neutral and ion state of the desired molecule at CBS-QB3 level of theory. The ms-TPE spectra were analyzed in the double harmonic approximation using the Franck-Condon approach as implemented in ezSpectrum or Gaussian1613. Ions generated from direct ionization of the molecular beam have a characteristic momentum component along the molecular beam axis and are imaged off-center on the detector. This enables separation from ionization of the background scattered gas in the ionization chamber as well as helps to distinguish dissociative ionization. The photon energies for the mass spectra were chosen to be higher than the ionization energy of species of interest, but below any dissociative photoionization threshold of larger species that may yield the same mass-to-charge ratio (m/z) fragment ions. Therefore, the ion TOF always corresponds to the mass of the neutral species, while fragmentation is suppressed quantitatively.
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Fig. S17. Mass spectra of species at the reactor outlet detected by operando PEPICO spectroscopy using different photon energies. Species: m/z 2 (H2), m/z 18 (H2O), m/z 28 (CO), m/z 30 (HCHO), m/z 40 (Ar), m/z 44 (CO2). Reaction conditions: ZnO weight, 20 mg; 450 °C; MeOH/Ar molar ratio, 1:3.4; FT
= 22 cm3 STP min−1; 50 kPa.
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Fig. S18. Mass spectra of atomic Zn detected by operando PEPICO spectroscopy. Reaction conditions: ZnO weight, 20 mg; 450 °C; MeOH/Ar molar ratio, 1:3.4; FT = 22 cm3 STP min−1; 50 kPa. Zn isotopes distribution: m/z 64 (49.17%), m/z 66 (27.73%), m/z 67 (4.04%), m/z 68 (18.45%), m/z 70 (0.61%).
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Fig. S19. Mass spectra of species over HZ140 at 450 °C by operando PEPICO spectroscopy using different photon energies. The incomplete methanol conversion may be related to the PIPECO setup and sample loading method: the quartz reactor is placed in a vacuum chamber and the powder samples are packed loosely to facilitate intermediates diffusion. Reaction conditions: HZ140 weight, 20 mg;
MeOH/Ar molar ratio, 1:3.4; FT = 22 cm3 STP min−1; 50 kPa. IE values of ethene, formaldehyde, methanol, propene, and dimethyl ether have been previously reported by us10. IE values of 1-butene, 2- butene, C5=, C6=, C7=, xylene and ethylbenzene are obtained from the National Institute of Standards and Technology (NIST) Mass Spectrometry Data Center.
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Fig. S20. Mass spectra of species over ZnO+HZ140 at 450 °C by operando PEPICO spectroscopy using different photon energies. Metallic Zn was not detected, as illustrated by green dash rectangular.
Reaction conditions: ZnO or HZ140 weight, 20 mg; MeOH/Ar molar ratio, 1:3.4; FT = 22 cm3 STP min−1; 50 kPa. IE values of ethene, formaldehyde, methanol, propene, dimethyl ether, butadiene, benzene, and toluene have been previously reported by us10. IE values of 1-butene, 2-butene, C5=, C6=, xylene and ethylbenzene are obtained from the National Institute of Standards and Technology (NIST) Mass Spectrometry Data Center.
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Fig. S21. Mass spectra of species over HZ140 at 500 °C by operando PEPICO spectroscopy using different photon energies. Reaction conditions: HZ140 weight, 20 mg; MeOH/Ar molar ratio, 1:3.4; FT
= 22 cm3 STP min−1; 50 kPa. IE values of ethene, formaldehyde, methanol, propene, dimethyl ether, benzene, and toluene have been previously reported by us10. IE values of 1-butene, 2-butene, cyclopentadiene, cyclopentene, C5=, cyclohexadiene, cyclohexene, C6=, methylcyclohexene, C7=, methylcyclohexane, xylene and ethylbenzene are obtained from the National Institute of Standards and Technology (NIST) Mass Spectrometry Data Center. IE values of methylclohexadiene, dimethylcyclohexadiene and ethylcyclohexadiene are obtained from theoretical calculation.
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Fig. S22. Mass spectra of species over ZnO+HZ140 at 500 °C by operando PEPICO spectroscopy using different photon energies. Reaction conditions: HZ140, 20 mg; ZnO, 20 mg; MeOH/Ar molar ratio, 1:3.4; FT = 22 cm3 STP min−1; 50 kPa. IE values of ethene, formaldehyde, propene, butadiene, acetone, benzene, and toluene have been previously reported by us10. IE values of 1-butene, 2-butene, xylene and ethylbenzene are obtained from the National Institute of Standards and Technology (NIST) Mass Spectrometry Data Center.
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Fig. S23. Photoion mass-selected threshold photoelectron (ms-TPE) spectra for different m/z values over ZnO+HZ140 at 500 °C as determined by operando PEPICO spectroscopy. (a) Ethene, (b) formaldehyde, (c) propene, (d) dimethyl ether, (e) 1,3-butadiene, (f) butenes, (g) bezenze, (h) toluene, and (i) xylenes. Both the experimental ms-TPE spectra (open squares, black lines) and theoretical reference spectra (solid lines with colors) of the identified species are shown. Reaction conditions: HZ140, 20 mg;
ZnO, 20 mg; MeOH/Ar molar ratio, 1:3.4; FT = 22 cm3 STP min−1; 50 kPa.
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Fig. S24. Scheme of methanol conversion to monocyclic aromatics over HZ140.
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Fig. S25. Scheme of methanol conversion to monocyclic aromatics over ZnO+HZ140. The species enclosed by the grey rectangule were not deteced due to their fast transformation into monoaromatics.
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Fig. S26. 1D 1H-13C cross-polarization (CP) MAS ssNMR spectra of trapped species over different catalysts using 13CH3OH feedstock. Reaction conditions: HZ140, 20 mg; ZnO, 20 mg; 450 °C; FT = 20 cm3 STP min−1; 0.1 MPa.
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Fig. S27. 2D correlation MAS ssNMR results over ZnO. (a) 2D 13C-13C and 1H-13C MAS ssNMR spectra of trapped species. (b) Assignment of observed hydrocarbons14.
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Fig. S28. MAS ssNMR spectra of trapped species over ZnO+HZ140. 1-D 1H-13C cross-polarization (CP, red) to probe rigid molecules (strongly adsorbed in catalyst). 1-D 13C direct excitation (DE, black) to probe all chemical species, including both strongly and weakly adsorbed species. The inset displays the structure of dimethoxymethane (DMM) which was detected in the DE spectrum (indexed by a dashed blue circle). The appearance of DMM as a weakly adsorbed species possibly originates from the reaction between HCHO and (CH3)2O (DME).
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Fig. S29. 2D correlation MAS ssNMR results over ZnO+HZ140. (a) 2D 13C-13C and 1H-13C MAS ssNMR spectra of the trapped species. (b) Magnified spectrum of formate species as indicated by the red rectangle in image (a). (c) Assignment of observed hydrocarbons15.
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Figure S30. Detailed 2D correlation MAS ssNMR results on the aromatics over the mixture. (a) 2D
13C-13C and (b) 1H-13C MAS ssNMR spectra of trapped species. (c) Assignment of aromatics.
Supplementary Note 6│The samples for NMR study were prepared using a Linkam cell (THMS600) equipped with a temperature controller. 13CH3OH was vaporized at 25 °C under N2 atmosphere and dosed by a digital mass flow controller into the reactor cell. The catalyst was dried in N2 flow at 500 °C for 1 hour prior to operating experiments. After reaction for 2 hours, the gas flow was stopped immediately (no purging). At the same time, the heating was stopped, and the reactor was quickly cooled down.
NMR data disclose that the details of CH3OH aromatization processes differ within different catalysts.
Using ZnO as catalyst, HCHO was first produced via dehydrogenation. Aldol condensation reactions could lead to the formation of longer unsaturated aldehydes. After decarboxylation, polyene species were formed thereof. Possibly due to the absence of acid sites, the cyclization reaction was not facilitated. As a result, only a tiny number of aromatics were observed, and most trapped species were methylated polyenes. Using zeolite as catalyst, olefins were first produced, which can undergo oligomerization, cyclization, hydrogen-transfer reactions to form aromatics. Using the mixture as catalyst, HCHO was produced. However, the absence of polyene indicates that the in-situ generated HCHO tended to form aromatics differently. A possible pathway was to react with olefins to form dienes, which can be transformed into aromatics facilely.
39
Fig. S31. Screening of the catalyst placed in the lower bed for catalysis relay. (a) HZ15 (Si/Al = 15), (b) ZnHZ15 (Si/Al = 15; Zn loading, 1.1 wt.%). (c) HZ12 (Si/Al = 12). (d) ZnHZ12 (Si/Al = 12; Zn loading, 3.5 wt.%). Reaction conditions: 450 °C; MeOH rate, 0.04 g h-1; MeOH/N2 molar ratio, 1:3; 0.1 MPa. Note that the weight of catalyst (20 mg) in the lower bed for catalyst screening is different from the optimized amount (40 mg) as shown in the main content (Fig. 4).
40
Fig. S32. Dehydrogenation ability test using propane as reactant. (a) Conversion of propane at 550
°C. (b) Product distribution (c) Conversion of propane on H-form zeolites at 550 °C. (d) Correlation between the catalyst activity and the concentration of Brønsted acid sites (BASs). (e) Catalytic activity of ZnHZ12 after subtracting the contribution of BASs. Reaction conditions: catalyst weight, 20 mg; 550 °C;
propane rate (20% in N2), 1200 ml h-1; 0.1 MPa. (f) Conversion of propane at 450 °C.
Supplementary Note 7│The different dehydrogenation abilities between ZnO, HZ140, and ZnHZ12 can be reflected by their catalytic performance in propane dehydrogenation (PDH). At 550 °C (a typical reaction temperature for PDH), ZnO and HZ140 show limited activity, with the conversion being 1.4%
and 1.7%, respectively. In contrast, ZnHZ12 shows a conversion value of 59.1% at TOS = 2 h. As the gradual deactivation caused by coke formation, the conversion decreases with TOS. Meanwhile, the selectivity to propylene increases due to the suppression of olefin transformation into other products. The contribution of Brønsted acid sites (BASs) to propane conversion cannot be ignored at 550 °C, and therefore we studied the propane conversion on three H-form zeolites with different Si/Al ratios (HZ140, Si/Al = 140; HZ40, Si/Al = 40; HZ12, Si/Al = 12). The conversions are stable during the 12-hour test.
The ratio between cracking products (C2H4+CH4) and dehydrogenation product (C3H6) is around 3.1~3.4, consistent with the previous report16. A pseudo linear correlation is found between the activity and the concentration of BASs (determined by pyridine-IR). For ZnHZ12, after subtracting the contribution of BASs to the activity, we found that it still shows high activity in PDH. The different dehydrogenation abilities of catalysts are also proved by performing the tests at 450 °C (the same temperature as for methanol aromatization). In summary, the stronger dehydrogenation ability of ZnHZ12 could explain it can be used to convert remaining olefins into aromatics. With the consumption of formaldehyde in the upper bed, adding more ZnO+HZ140 cannot further increase the aromatic selectivity, and therefore catalysis relay is necessary.
41
Fig. S33. Comparison between this work and previous works on both aromatic selectivity and catalyst lifetime for the methanol-to-aromatic process. The origin of data can refere to Table S4.
42
SIII │Supplementary Tables
Table S1. Average selectivity to aromatics (10 hours of reaction) at different reaction temperatures.
The catalyst packing modes correspond to Figure S1.
400 °C 450 °C 500 °C
Zeolite 12.5% 10.2% 9.8%
ZnO // Zeolite, dual bed 12.6% 22.5% 36.3%
ZnO + Zeolite, granules mixture 28.3% 38.2% 32.2%
ZnO + Zeolite, powder mixture 29.1% 39.1% 29.7%
Table S2. Product distribution at 450 °C (10 hours of reaction) over different catalysts. The catalyst packing modes correspond to Figure S1.
COx CH4 C2-C4= C2-C4 C5-C7 Aromatic s
Zeolite 0 0.4% 73.4% 7.9% 8.1% 10.2%
ZnO // Zeolite, dual bed 34.7% 4.0% 34.9% 1.5% 2.4% 22.5%
ZnO + Zeolite, granules mixture 0 1.6% 52.8% 4.4% 3.0% 38.2%
ZnO + Zeolite, powder mixture 0 1.2% 52.5% 3.0% 4.2% 39.1%
Table S3. Product distribution at 450 °C (10 hours of reaction) for ZnO+HZ140//ZnHZ12.
CH4 C2-C4= C2-C4 C5-C7 Aromatics
3.4% 12.7% 12.8% 0.8% 70.4%
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Table S4. Strategies comparison between this work and previous works, corresponding to Fig. S33.
Catalyst Name Strategy employed Aromatics
selectivity a BTX percentage
Catalyst
lifetime b Origin of work c
ZnO+HZ140//ZnHZ12
Inexpesive and commercially
available materials,
formaldehyde-assisted aromatics formation, catalysis relay, and precise location control of active sites.
72% 91% > 400 h
(100%) This work.
Zn(DS)/ZSM5 Bottom-up synthesis of Zn-ZSM-
5 with small particle size. 43% - 145 h
(60%)
MMM, 2014, 197, 252.
GaCNT-HZ Bottom-up synthesis of Ga-ZSM-
5 with hierarchical pores. 73% 77% 17 h
(70%)
IECR, 2019, 58, 7948.
Zn(IE)/ZSM-5 Bottom-up synthesis of ZSM-5,
and then ion-exchanging with Zn. 47% - 70 h
(60%)
MMM, 2014, 197, 252.
Zn/Z-ST400 Ion-exchanging with Zn and then
steaming treatment of ZSM-5. 56% 80% 103 h
(50%)
FPT, 2017, 162, 66.
Zn(IM)/ZSM-5 Bottom-up synthesis of ZSM-5,
and then impregnation with Zn. 43% - 50 h
(60%)
MMM, 2014, 197, 252.
Zn/HZ-0.25 Bottom-up synthesis of Zn-ZSM-
5 with small particle size. 46% - 100 h
(60%)
FPT, 2017, 157, 99.
Zn/NZS-60 Bottom-up synthesis of Zn-ZSM-
5 with small particle size. 68% 30% 75 h
(60%)
JMCA, 2014, 2, 19797.
bayberry-like ZnO/ZSM5
Bottom-up synthesis of Zn-ZSM-
5 with hierarchical pores. 64% - 7.5 h
(70%)
CC, 2016, 52, 2011.
MZnZSM-5-2 Bottom-up synthesis of Zn-ZSM-
5 with hierarchical pores. 43% 71% 117 h
(78%)
RSCA, 2016, 6, 23428.
Zn/MFI NRAs Bottom-up synthesis of Zn-ZSM-
5 with hierarchical pores. 70% - 60 h
(80%)
JMCA, 2016, 4, 10834.
Zn/ZSM-5-AP60 Bottom-up synthesis of Zn-ZSM-
5 with small particle size. 62% - 55 h
(50%)
CST, 2014, 4, 3840.
40-ZnO/HZSM5 Zn-ZSM-5 prepared with atomic
layer deposition. 68% 88% 35 h
(50%)
CST, 2016, 6, 3074.
4%-Ga-HZ-5 Ga-ZSM-5 prepared with
impregnation, and cofeeding n- butanol to increase test stability.
58% 78% 50 h
(99%)
ACSC, 2018, 8, 1352.
Z-25 CO cofeeding at high pressure up
to 4 MPa. 80% 65% 9 h
(70%)
ACIE, 2018, 57, 12549.
Zn/H-ZSM-5 Zn-ZMS-5 prepared with
impregnation. 73% 48% 10 h
(80%) JEC, 2021, 54, 174.
Zn@ZSM-5 Zn-ZSM-5 prepared with alkaline treatment, Zn impregnation, and then dry gel synthesis.
65% - 40 h
(90%)
MMM, 2021, 312, 110696.
Platelike HZSM5 Bottom-up synthesis of ZSM-5 with short-b axis, fluoride- assisted synthesis.
18% - 280 h
(90%) JACS, 2021, 143, 1993.
8(Z220) / 2(ZnZ30) Two-step MTA conversion, with
light olefins as a bridge. 40% - 76 h
(85%)
ACB, 2021, 291, 120098.
HZ280 High-pressure operation at 3
MPa. 50% 40% 80 h
(80%)
ACSC, 2021, 11, 3602.
ZSM-5 nanoboxes Bottom-up synthesis, then etching
and recrystallization. 35% 77% 35 h
(80%) ACIE, 2022, 61, e202200677 Z480/Z240/Z120/ZnZ60 Multiple layers of ZSM-5 with
gradient-increasing acidity. 33% 50% 170 h
(95%) Fuel, 2022, 315, 123241.
Zn/(S1@Z5@S1)
Hollow triple-shelled Zn-ZSM-5 prepared by serial crystallization, etching, recrystallization, and Zn impregnation.
56% 82% 40 h
(100%)
ACIE, 2022, 61, e202114786.
44
Note: a Aromatics includes BTX and C9+ monoaromatics, and the selectivity refers to that at the early stage of a reaction. b X h (Y
%) stands for a reaction lasting for X hours before the methanol conversion decreases to Y%. c Journal names: MMM, Microporous and Mesoporous Materials; IECR, Industrial & Engineering Chemistry Research; FPT, Fuel Processing Technology; JMCA, Journal of Materials Chemistry A; CC, Chemical Communications; RSCA, RSC Advances; CST, Catalysis Science and Technology; ACSC, ACS Catalysis; ACIE, Angewandte Chemie International Edition; JEC, Journal of Energy Chemistry; JACS, Journal of the American Chemical Society; ACB, Applied Catalysis B: Environmental; Fuel, Fuel.
45
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